This invention relates to devices for the administration of a powdered substance by inhalation, and in particular, to a device for administering powdered medicaments to the lungs of a user.
Various types of inhalers for delivering a medicament are known. For example, U.S. Pat. No. 3,938,516 (Mathes No. 1) discloses an inhaler for delivering a powdered medicament. The device includes a mouth piece 14 which has provided therein an emptying chamber. A longitudinally extending passageway for introducing air into the inhaler is connected to the passageway. The inhaler also includes a hollow air stream tube which extends preferably into an opened capsule containing a medicament. Upon inhalation, air drawn through the air stream tube into the capsule assists in causing the medicament to be expelled therefrom.
Mathes No. 1 states at column 4, lines 32-45, that xe2x80x9cQuite obviously, no single device will be suitable for all persons requiring administration of powdered medicaments since, for example, people with differing lung capacities are known to generate flow rates from about 30 liters/minute or so to about 120 liters/minute or so through inhalation devices of this and known types. Nonetheless, the device of [Mathes No. 1] affords such variability, through proper selection of the various design parameters, that a device, embraced with the scope of [Mathes No. 1], can be designed for a particular patient-generated flow rate to deliver the medicament according to a certain set of pre-determined objectives (e.g., slow or fast administration, one or more inhalations etc.).xe2x80x9d
Accordingly, one of the disadvantages of Mathes No. 1 is that a single device is not capable of being used with a variety of patients. In some cases, the inhaler may be required for treating an individual who has a diminished lung capacity. For example, an individual who may need to use the device may suffer from, for example, emphysema or asthma, and may not be able to generate a high flow rate of air. Therefore, the device of Mathes No. 1 would have to be designed for someone who could only administer a dose slowly due to their diminished lung capacity. Alternately, the device may be used by someone who does not have a diminished lung capacity. Unless the device is properly designed, the medicament will exit the inhaler at a rate such that a portion, if not substantially all of the medicament, will impact upon the throat and airways of the user and therefore not be drawn into the lungs for absorption.
A further disadvantage of Mathes No. 1 is that, over the course of a single inhalation, the concentration of the medicament in the air inhaled by a user is uneven. This arises for two reasons. First, once the medicament is withdrawn from the container, it is immediately transported through the inhaler into the mouth or nose of the user. Therefore, little mixing of the medicament in the air inhaled by the user occurs. This results in uneven distribution of the powder in the air inhaled by the user and, to the extent that the medicament is drawn into the lungs of the user, the medicament will not be distributed evenly throughout the lungs. Secondly, a substantial portion of the medicament may be withdrawn from the medicament container and entrained in the air upon initial inhalation. Accordingly, the medicament will not be distributed throughout the entire lung of the user but will be concentrated in that portion of the lungs of the user to which the first portion of the air inhaled on inhalation travels. (See also U.S. Pat. No. 4,014,336 (Mathes No. 2); U.S. Pat. No. 4,005,711 (Glen No. 1); and U.S. Pat. No. 4,098,273 (Glen No. 2).) In Glen Nos. 1 and 2, a deflector surface is used to direct a portion of the incoming air into the medicament container so as to entrain the medicament in the air which is inhaled by a user.
U.S. Pat. Nos. 3,964,483 (Mathes No. 3) and U.S. Pat. No. 3,973,566 (Mathes No. 4) each disclose a device wherein the air entering the inhaler is not aimed directly at the medicament in a medicament container. Instead, turbulent air flow is created so as to draw the medicament out from the container. These devices have the same disadvantages as Mathes No. 1.
In accordance with the instant invention, there is provided an inhalation device for use in delivering a powdered substance to a user. The inhalation device comprises a holding portion for holding the substance, an air entry passageway, a hold-up chamber and an air exit passageway. The air entry passageway is sized and configured to direct air entering the inhalation device at the holding portion and to fluidize the substance upon inhalation by the user.
In one embodiment, the air entry passageway includes an inlet port, an exit port and a cross-sectional flow area. The exit port is proximate to and directed at the holding portion. The hold-up chamber is in flow communication with the holding portion. The air exit passageway preferably includes an inlet port in flow communication with the hold-up chamber, an exit port and a cross-sectional flow area. The cross-sectional flow area of the exit passageway is preferably greater than the cross-sectional flow area of the air entry passageway.
In a preferred embodiment of the invention, the inhalation device includes a plurality of air entry passageways, with at least one of the air entry passageways directed at the holding portion. The number and cross sectional flow area of the air entry passageways may be selected to cause the air entering the inhalation device through the air entry passageways to travel at a velocity to fluidize a major portion of the powdered substance, preferably a medicament, upon the commencement of inhalation by the user. In a more preferred embodiment, substantially all of the powdered substance is fluidized upon commencement of the inhalation by the user. The combined cross-sectional flow area of the plurality of air entry passageways is preferably less than the cross-sectional flow area of the air exit passageway.
Accordingly, one advantage of the instant invention is that the air entering the inhaler effectively forms a jet directed to impinge upon the powdered substance in the inhaler so as to cause the substance to effectively immediately fluidize during the first stage of inhalation by the user. The fluidized substance is then drawn into the hold-up chamber where it is effectively stored in a fluidized state during the remainder of the inhalation. This produces three advantages.
First, the powdered substance is effectively deaggregated almost immediately upon inhalation so as to form a relatively uniform concentration of substance in the hold-up chamber at the commencement of inhalation. As air is drawn through the air exit passageway by the user, a relatively constant concentration of substance is initially drawn into the lungs of the user. The fluidized substance is thereafter diluted over time as more air is drawn into the hold-up chamber. Therefore, the concentration of the first portion of the fluidized substance initially inspired by the user will be greater than the subsequent portions, which helps to provide a more even deposition of the substance in the lungs of the user.
Secondly, the deaggregation of the particles by the air travelling through the air entry passageways reduces the likelihood of large particles of substance being present and impacting upon the throat and/or upper airways of the user.
A third advantage is that the relatively even concentration of substance in the hold-up chamber is formed almost immediately upon inhalation so that even the first air drawing into the lungs of the user contains a diluted fluidized mass of substance. Further, as the inhalation continues, additional air is introduced through the air entry passageways into the hold-up chamber to mix with the remaining fluidized substance. Therefore, as the inhalation continues, the substance is continuously drawn into the lungs. Thus, the substance is drawn into a large volume of the lung.
In one embodiment, substantially all of the air entering the inhalation device is directed at the powdered substance. In a further alternate embodiment, all of the air entering the inhalation device is directed at the substance.
The air exit passageway is preferably sized, with a cross-sectional flow area greater than the cross-sectional flow area of the combined air entry passageways, to provide the fluidized substance leaving the inhalation device with a velocity sufficiently low for a major proportion of the substance not to impact on the throat and upper airways of the user but to be drawn into the lungs and/or lower passageway of the user. The air which enters the inhalation device at a rapid velocity through the air entry passageways may decrease in velocity as it enters the hold-up chamber. The air may then be drawn off from the hold-up chamber at a controlled rate so as to provide a velocity of the fluidized substance leaving the hold-up chamber (through the air exit passageway) which is sufficiently low for the substance to be drawn into the lungs of the user.
The air entry passageway and/or the lower portion of the hold-up chamber are configured to introduce air into the hold-up chamber such that the air entering the inhalation device will rotate, swirl or travel around the hold-up chamber to maintain the substance in a fluidized state. In one embodiment, the hold-up chamber has interior walls which are substantially smooth and are of generally uniform cross-section. Accordingly, the hold-up chamber is preferably configured to permit cyclonic flow of air within the hold-up chamber and the air entry passageway and/or the lower portion of the hold-up chamber are configured to initiate cyclonic flow of air upon inhalation by the user. The cyclonic flow of air may assist in further deaggregation of the powdered substance and in maintaining the deaggregated substance in a fluidized state.
The air exit passageway is preferably positioned in the hold-up chamber at a position which is distal to the holding portion which receives the powdered substance. In one embodiment, the hold-up chamber is cylindrically shaped and has a longitudinally extending axis around which the air inhaled by a user rotates or swirls with the air exit passageway positioned on the cylindrically shaped wall of, and in flow communication with, the hold-up chamber. In this embodiment, the hold-up chamber extends longitudinally away from the holding portion which receives the powdered substance to the air exit passageway. The air exit passageway preferably extends outwardly from the hold-up chamber at an angle to the longitudinal direction of the hold-up chamber. More preferably, this angle is about 90xc2x0 (i.e. transverse to the axis of rotation of the air in the hold-up chamber).
In another embodiment, the hold-up chamber further includes a frusto-conically shaped portion extending from the cylindrical portion. A bottom of the frusto-conically shaped portion communicates with the holding portion. The shape of the frusto-conically shaped portion facilitates the cyclonic flow of fluidized substance within the hold-up chamber.
In addition, in those embodiments including a plurality of air entry passageways, one or more of the plurality may be configured to direct air at the powdered substance and one or more of the air entry passageways may be configured to direct air so as to promote the cyclonic rotation of air in the hold-up chamber.
A further advantage of the instant invention is that high velocity air may be used to extract the powdered substance from a reservoir to mix the medicament with air and to segregate or deaggregate the substance. Further, this extraction, mixing and deaggregation may be achieved by inspiratory effort alone. No battery operated impellers or other mechanical devices need be included. Further, by utilizing a plurality of air entry passageways which, in total, have a relatively low cross-sectional area, these high velocities can be achieved using low inspiratory flow rates.
A further advantage is that the dosage which is withdrawn is less dependent on inspiratory flow rates than other known devices. Accordingly, the dose of powdered substance, preferably a medicament, which is withdrawn from the inhalation device is more consistent than may be achieved with other known devices. Further, due to the low velocity of substance as it exits the inhalation device, relatively low amounts of substance will be deposited in the throat and upper airways of the user. Not only does this result in more substance being drawn into the lungs of the user, where in general it is more easily absorbed by the body, it may cause less irritation to the throat and upper airways of the user.